Air bleed system for hydraulic piston



May 2, 1967 R. G. ELLIS AIR BLEED SYSTEM FOR HYDRAULIC PISTON Filed Sept. 8, 1965 2 Sheets-Sheet l 1 &

Sens: n9 1 INVENTOR.

17 7 roam/7 y 2, 1967 R. G. ELLIS 3,316,817

AIR BLEED SYSTEM FOR HYDRAULIC PISTON Filed Sept. 8, 1965 2 Sheets-Sheet 2 j T I5!" 70' .45 '4 50 M I l I M l I )1 I do] I I i 35 id 1 j 47 H $1 $2 I f M J; I I I g INVENTOR.

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United States Patent ice 3,316,817 AIR BLEED SYSTEM FOR HYDRAULIC PISTQN Rollo G. Ellis, Birmingham, Mich, assignor to Elox Corporation of Michigan, Troy, Mich, a corporation of Michigan Filed Sept. 8, 1965, Ser. No. 485,787 3 Claims. (Cl. 92--79) This invention relates to hydraulic motors and, more particularly, to an air bleed system for incorporation.

therein.

One major problem encountered in hydraulic motors arises from the accumulation of air particularly where the hydraulic motor cylinder is maintained in a vertical position. Due to the action of the pump and the system, a substantial quantity of air is caused to accumulate in the system localized around and extending below the lower piston face. During the operation of the hydraulic motor and system, the air accumulated in the system tends to assume the relatively high pressure of the system which may be as high as 600 p.s.i. When the pump is turned off, the entrapped air becomes reduced to atmospheric pressure i.e., approximately 14.7 p.s.i. This causes an expansion of the air chamber below the lower piston face to approximately forty times its original size. When the hydraulic motor is incorporated, for example, in a machine tool, it is frequently utilized to position the head and tool vertically over the workpiece. if the head and piston are released before the pump is started into opera tion, there occurs a sudden settling of the head over a substantial drop so that tool and workpiece damage frequently results. Periodic servicing of the motor is necessary by way of bleeding the air accumulated in the lower end of the cylinder.

The present invention provides an air bleed system which is incorporated in the piston and permits a continual passage of fluid containing entrained air from beneath the lower piston end to positively prevent acculation of any appreciable amount of air in the system.

Accordingly, it will be seen that the object of the present invention is to provide an improved air bleed sys tem which is continually operable to provide air bleeding during the reciprocal motion of the piston in a hydraulic motor.

In conformance with the foregoing object and others which will become apparent, the present invention in several alternate embodiments is shown and described in the following specification and drawings in which:

FIGURE 1 is a schematic drawing of a hydraulic servo system for a machine tool in which the present invention FIGURE 2 is a combined schematic drawing of a hydraulic motor incorporating my improved air bleed system together with a showing of the piston in longitudinal half section to best illustrate its components and their mode of construction; and

FIGURE 3 is a view essentially similar to that of FIGURE 2 in which an alternate and preferred embodiment of the air bleed system is illustrated.

With more specific reference to FIGURE 1, it will be seen that the hydraulic servo system includes a hydraulic motor including a cylinder 12 having a piston 14 mounted therein for reciprocal movement upwardly and downwardly. Piston 14 incorporates the air bleed system shown in block form and identified by numeral 16. Extending downwardly from the lower face of piston 14 is a rod 18 which supports at its lower end a tool holder 20 and electrode tool 22. An insulator 21 is mounted between rod 18 and holder 20. In the operation of the hydraulic servo system in an electrical discharge machine tool, the electrode 22 is maintained with an 3,316,817 Patented May 2, 1%67 optimum gap spacing between it and the workpiece 24 while a suitable machining power source 26 is connected across the gap to provide discrete electrical machining pulses thereacross as is well known in the electrical dis charge machining art. The hydraulic servo system further includes as its necessary elements a sensing and control circuit 28 and an electrohydraulic servo valve shown .in schematic form and identified by the numeral 30. Sensing and control circuit 28 is a circuit, one form of which may be seen in US. Patent No. Re. 25,580, entitled, Hydraulic Servo Feed and issued to Robert S. Webb on May 19, 1964. Responsive to an electrical gap parameter such as average voltage, a control signal is introduced from sensing and control circuit 28 to the control input terminals of servo valve 30 which terminals are shown as 32, 34 across servo valve control coils 33, 35. Depending upon the direction of current flow through a control fluid flow is furnished under pressure to the hydraulic motor through its input 36 located at the upper end of cylinder 12 or its input 38 located at the lower end of cylinder 12. The hydraulic circuit further includes a pump 4-0 which may be of the constant delivery type and which draws fluid from sump 42 and directs that fluid through conduit 44 to the input port 46 of servo valve 30. Relief valve 41 is included as shown with a return to sump 42. Exhaust port 48 is also provided in servo 3t] and connected as shown to conduit 50 to return fluid to sump 42. The control outlet ports 52 and 54 of servo valve 30 are connected to conduits 56 and 58 respectively to provide the necessary fluid outputs to the inlets 36 and 38 of the hydraulic motor 10. In the normal operation of the system, the fluid pressure is provided at the inlets 36, 38 of cylinder 12 varying according to the gap signals received from sensing and control circuit 28 as reflected to the control winding of servo valve 30. When a larger gap spacing is required, a relatively high fluid pressure is provided through input 38 against the lower face of piston 14 to cause the upward movement of electrode 22. When a closer gap spacing is required according to the signal output of sensing and control circuit 28, a relatively high fluid pressure is provided through the input 36 of motor 10 to provide downward movement of the piston 14 and of electrode 22.

FIGURE 2 shows the detail of an air bleed system according to the present invention in which a two'way check valve identified by the number 66 is mounted integral with piston 14. Conduit 64 is. provided from the periphery of piston 14 proximate its lower face. Conduit 64 is connected to an arcuate chamber 68 formed centrally in the piston. Conduit 70 extends between chamber 68 and chamber 72 which terminates at its upper end in the two-way check valve 6i). Included in the two-way check valve are upper and lower O-rings 74, 76 which are cooperable with a spherical closure or control element 78. The upper limit for O-ring 74 is provided by threaded plug 75 which plug has a central passage 77 extending thereth-rough and communicating between check valve 60 and the upper face of piston 14. It will be seen that, when the spherical closure element 78 moves between its upper and lower closed conditions and is in an intermediate position as illustrated, passage of fluid which ordinarily contains some entrained air is permitted to pass through the valve. It will further be seen that piston 14 in its construction comprises upper and lower cylinder portions 80 and 82 and central portion 84 which are so connected as to maintain a seal 86 in sealing engagement between the periphery of piston 14 and the inner cylinder wall of cylinder 12.

FIGURE 3 illustrates an alternate embodiment of the present invention in which the air bleed system is substantially simplified in its mode of construction. The

essential elements of piston 14 are the same as in FIG- U-RE 2 with conduit 64 communicating between the periphery of piston 14 proximate its lower piston face and. the lower end of a one-way check valve 88. Check valve- 88 includes a spherical closure element 90 and an upper arcuate seal embodied as O-ring 92. Provision is made for temporary accumulation of pressurized fluid including entrained air within arcuate chamber 94- which chamber is formed intermediate the upper deflectible portion of seal 86 and the inner cylinder wall of cylinder 12. A pin 95 is utilized to maintain alignment between lower and central piston portions 82 and 84 to maintain alignment of the parts and insure the proper seating of O-ring 92.

Description of operation The operation of the system of FIGURE 2 is to provide a continuous air bleed operation during the reciprocal movement of piston 14. During the upward and down- Ward movements of the piston 14 as has been indicated, a pocket of air becomes gradually accumulated at the pe riphery of piston 14 below seal 86 and proximate the lower piston face. During each downward movement of the piston, pressurized fluid containing the entrained air travels through conduit 64, conduit 70 and is permitted to accumulate in chambers 68 and 72. Further, during the downward movement of piston 14, with pressure applied at the upper piston face, spherical closure element 78 is maintained in sealing engagement with lower O-ring 76. When upward movement occurs, pressure is applied through inlet 38 against the lower face of piston 14 so that the air accumuated is pressurized to initiate an upward movement of spherical closure member 78 toward its sealing engagement with upper O-ring 74. During the movement of member 7 8 intermediate its lower and upper closed positions, pressurized fluid including entrained air is permitted to travel through check valve 60 and outwardly through passage 77 and the upper face of piston 14, thus eliminating any air entrapped. When pressure is again applied through inlet 36 against the upper face of piston 14, downward movement of the piston again occurs and the air bleed cycle is repeated.

The operation of the air bleed system of FIG. 3 has a basic similarity to that of the apparatus of FIGURE 2 except that .a one-way check valve is utilized which operates in conjunction with the upper deflectible portion of seal 85. A chamber for the temporary accumulation of pressurized air is provided in the annular chamber formed between seal 86 and the inner wall of cylinder 12. It will be seen that the apparatus in FIGURE 3 is much simpler in its construction and represents a preferred embodiment of the present invention. In the apparatus of FIGURE 3, when pressure is applied through inlet 36 against the upper face of piston 14, there is initiated a downward movement of the piston and spherical closure element 90 is permitted to drop downwardly from its sealing engagement with O-ring 92 to permit passage of air through conduit 64 and upwardly through check valve 88 for temporary storage in arcuate chamber 94 and passage 93. When upward pressure is applied through inlet 38 against the lower face of piston 14, spherical closure element 96) is forced into sealing engagement with O-ring 92. The upper deflectible portion of seal 86 which forms the upper enclosing member of arcuate chamber 94 is moved from engagement with the inner cylinder wall of cylinder 12 to permit leakage of fluid including entrained air from arcuate chamber 94 upwardly past the upper periphery and face of the piston 14. It will thus be seen that the upper deflectible portion of seal 86 itself performs the added function of a one-way check valve. The apparatus of FIGURE 3 like that of FIGURE 2 is thus effective to provide a continuously controlled bleeding of air accumulated at the lower face during operation of the motor.

While the present invention has been described with reference to its employment in a hydraulic servo feed system for a machine tool of the electrical discharge machining type, it will become clear that the invention is not limited to that environment but is susceptible to a wide variety of uses and applications in the hydraulic motor field.

I claim:

1. In a hydraulic motor including a cylinder and a piston mounted for reciprocal movement therein responsive to operating pressures applied, an air bleed system for said piston comprising at least one passage extending through the periphery of said piston proximate its lower face, a check valve having its body in said piston and its inlet communicating with said passage, a seal mounted about the periphery of said piston, said seal having an upper deflectible portion engageable with the inner wall of said cylinder and forming an arcuate chamber between said piston and said wall, said portion being deflectible toward and away from engagement with said inner wall responsive to the operating pressure supplied to said piston, said arcuate chamber being in communication with said check valve, said check valve having its control element movable to an open position during downward movement of said piston to permit flow of fluid including entrained air into said arcuate chamber, said deflectible portion operable to permit passage of air accumulated in said chamber upwardly therefrom responsive to upward movement of said piston.

2. In a hydraulic motor including a cylinder and a piston mounted for reciprocal movement therein, an air bleed system for said piston comprising at least one passage extending through the lower end of said piston, a seal having an upper deflectible portion for engagement with the inner wall of said cylinder and forming an arcuate chamber intermediate said piston and said inner wall, and a check valve operatively connected to said passage and said arcuate chamber for providing fluid flow including entrained air to said arcuate chamber during downward movement of said pitson and for providing fluid flow including entrained air from said arcuate chamber upwardly proximate the upper face of said piston responsive to the upward movement of said piston.

3. In a hydraulic motor including a cylinder inclined to the horizontal and a piston mounted for reciprocal movement therein responsive to operating pressures applied, an air bleed system for said piston comprising at least one passage extending through the periphery of said piston proximate its lower face, a seal mounted about the periphery of said piston, said seal having an upper deflectible portion normally engageable with the inner Wall of said cylinder and forming an arcuate chamber between said piston and said wall, a check valve having its body in said piston, its inlet communicating with said passage, and its outlet communicating with said chamber, said check valve having its control element movable downwardly to an open position during downward movement of said piston to permit flow of fluid including entrained air from said passage into said arcuate chamber, said deflectible portion movable from its engagement with said wall to permit passage of air accumulated in said chamber upwardly therefrom responsive to upward movement of said piston.

References Cited by the Examiner UNITED STATES PATENTS 2,268,624 1/1942 Schwarz 92-82 2,386,874 10/1945 Miner 92--82 2,452,369 10/ 1948 Gravenhorst et al. 9279 X 2,757,993 8/1956 Flick 92-244 X 3,224,378 12/1965 Graham 92-l82 X MARTIN P. SCHWADRON, Primary Examiner.

I. C. COHEN, Assistant Examiner. 

1. IN A HYDRAULIC MOTOR INCLUDING A CYLINDER AND A PISTON MOUNTED FOR RECIPROCAL MOVEMENT THEREIN RESPONSIVE TO OPERATING PRESSURES APPLIED, AN AIR BLEED SYSTEM FOR SAID PISTON COMPRISING AT LEAST ONE PASSAGE EXTENDING THROUGH THE PERIPHERY OF SAID PISTON PROXIMATE ITS LOWER FACE, A CHECK VALVE HAVING ITS BODY IN SAID PISTON AND ITS INLET COMMUNICATING WITH SAID PASSAGE, A SEAL MOUNTED ABOUT THE PERIPHERY OF SAID PISTON, SAID SEAL HAVING AN UPPER DEFLECTIBLE PORTION ENGAGEABLE WITH THE INNER WALL OF SAID CYLINDER AND FORMING AN ARCUATE CHAMBER BETWEEN SAID PISTON AND SAID WALL, SAID PORTION BEING DEFLECTIBLE TOWARD AND AWAY FROM ENGAGEMENT WITH SAID INNER WALL RESPONSIVE TO THE OPERATING PRESSURE SUPPLIED TO SAID PISTON, SAID ARCUATE CHAMBER BEING IN COMMUNICATION WITH SAID CHECK VALVE, SAID CHECK VALVE HAVING ITS CONTROL ELEMENT MOVABLE TO AN OPEN POSITION DURING DOWNWARD MOVEMENT OF SAID PISTON TO PERMIT FLOW OF FLUID INCLUDING ENTRAINED AIR INTO SAID ARCUATE CHAMBER, SAID DEFLECTIBLE PORTION OPERABLE TO PERMIT PASSAGE OF AIR ACCUMULATED IN SAID CHAMBER UPWARDLY THEREFROM RESPONSIVE TO UPWARD MOVEMENT OF SAID PISTON. 